This invention relates to electrical device coil forms and, more particularly, it relates to a coil form produced from fiber reinforced resin material.
The market segment for electrical devices such as for windings of motors, transformers and solenoids is increasingly moving to miniaturization of such devices. This in turn leads to a rise in internal equipment operating temperature resulting in a need for higher temperature ratings on insulation materials used for these applications.
Coil forms fashioned from Nomex.RTM. aramid paper, a high temperature resistant paper with excellent physical and electrical properties are known for use in high temprature (greater than 200.degree. C. rating of UL Standard 1446) wherein a coil of wire is wound over the Nomex.RTM. paper coil form placed on a mandrel to support the form. However, this product does not exhibit a high degree of structural strength and the wire coil must be wound fairly loosely over the Nomex.RTM. paper coil form or the Nomex.RTM. will implode after the wire windings are in place and the winding mandrel is removed. The use of this coil form system is labor intensive, requires more wire than necessary and provides lower transformer efficiency.
Insulation systems approved to UL Standard 1446 are rated by subjecting them to cycles of thermal aging, low temperature shock, humidity and vibration. At the end of each cycle the systems are checked at 600 volts for short circuits, with the cycle being repeated until the insulation breaks down. Test voltages may be higher for systems with higher operating voltages. The temperature rating assigned to an insulation system will depend on the service life of the equipment at different aging temperatures.